H.320 or Narrow-band visual telephone systems and terminal equipment is an ''umbrella Recommendation'' by the

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Comm ...

for running Multimedia (Audio/Video/Data) over

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

based networks. The main protocols in this suite are H.221, H.230, H.242,

audio codecs An audio codec is a device or computer program capable of encoding or decoding a digital data stream (a codec) that encodes or decodes audio. In software, an audio codec is a computer program implementing an algorithm that compresses and decompres ...

such as

G.711 G.711 is a narrowband audio codec originally designed for use in telephony that provides toll-quality audio at 64 kbit/s. G.711 passes audio signals in the range of 300–3400 Hz and samples them at the rate of 8,000 samples per second ...

( PCM) and G.728 (

CELP Code-excited linear prediction (CELP) is a linear predictive speech coding algorithm originally proposed by Manfred R. Schroeder and Bishnu S. Atal in 1985. At the time, it provided significantly better quality than existing low bit-rate algori ...

), and discrete cosine transform (DCT)

video codecs The following is a list of compression formats and related codecs. Audio compression formats Non-compression * Linear pulse-code modulation (LPCM, generally only described as PCM) is the format for uncompressed audio in media files and it is al ...

such as

H.261 H.261 is an ITU-T video compression standard, first ratified in November 1988. It is the first member of the H.26x family of video coding standards in the domain of the ITU-T Study Group 16 Video Coding Experts Group (VCEG, then Specialists Gro ...

and H.263. It is formally named as ''

Narrow-band Narrowband signals are signals that occupy a narrow range of frequencies or that have a small fractional bandwidth. In the audio spectrum, narrowband sounds are sounds that occupy a narrow range of frequencies. In telephony, narrowband is usu ...

visual telephone systems and terminal equipment''. It specifies technical requirements for narrow-band visual telephone systems and terminal equipment, typically for

videoconferencing Videotelephony, also known as videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio and video signals by people in different locations for real time communication.McGraw-Hill Concise Ency ...

and

videophone Videotelephony, also known as videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio and video signals by people in different locations for real time communication.McGraw-Hill Concise Ency ...

services. It describes a generic system configuration consisting of a number of elements which are specified by respective ITU-T Recommendations, definition of communication modes and terminal types, call control arrangements, terminal aspects and interworking requirements.ITU-T (2004-03) (PDF
H.320 : Narrow-band visual telephone systems and terminal equipment
Retrieved on 2009-07-21 The service requirements for visual telephone services are presented in ITU-T Recs F.720 for videotelephony and F.702 for videoconference. Video and audio coding systems and other technical aspects common to audiovisual services are covered in other Recommendations in the H.200/F.700-series. Narrow-band for this specification is defined as bit rates ranging from 64 kbit/s to 1920 kbit/s. This channel capacity may be provided as a single B/H0/H11/H12-channel or multiple B/H0-channels in ISDN. Used video codecs: H.261, and optionally H.262, H.263,

H.264 Advanced Video Coding (AVC), also referred to as H.264 or MPEG-4 Part 10, is a video compression standard based on block-oriented, motion-compensated coding. It is by far the most commonly used format for the recording, compression, and distr ...

according to the video hierarchy specified in specification, and in ITU-T Recs H.241 and H.242. H.261 is mandatory in any enhanced H.320 system with video capability. Baseline H.263 capability shall be required in systems that use enhanced video modes. Used audio codecs: G.711, and optionally

G.722 G.722 is an ITU-T standard 7 kHz wideband audio codec operating at 48, 56 and 64 kbit/s. It was approved by ITU-T in November 1988. Technology of the codec is based on sub-band ADPCM (SB-ADPCM). The corresponding narrow-band codec based on ...

, G.728, G.723.1,

G.729 G.729 is a royalty-free narrow-band vocoder-based audio data compression algorithm using a frame length of 10 milliseconds. It is officially described as ''Coding of speech at 8 kbit/s using code-excited linear prediction'' speech coding (CS-ACEL ...

. (Example of usage: If a visual telephone interworks with a wideband speech terminal, G.722 audio may be used instead of G.711 audio.)

References

External links

ITU-T website

ITU-T H.320 : Narrow-band visual telephone systems and terminal equipment
- technical specification Integrated Services Digital Network Videotelephony ITU-T recommendations ITU-T H Series Recommendations {{telecomm-stub

See also

References

External links